This invention relates to the field of machine safeguarding devices, and more specifically to the field of lockout devices for allowing multiple users to control energization of systems.
There are many tasks where a person or persons must enter the dangerous workspace of a robot or other system. Examples of such tasks include machine maintenance, product quality inspection, process monitoring, and management inspection. Often, the operation of the system can be hazardous to humans, either by physical contact with dangerous parts (e.g., cutting tools, lifts and presses) or by dangerous environmental conditions (e.g., extreme temperatures, airborne chemicals). For safety, therefore, the system must be prevented from operating while people are within the potentially hazardous space (the controlled space). This is often accomplished with barriers and doors that prevent system operation when opened. To restart the system, the barrier or door must be closed. Additional external resets are sometimes required.
Unfortunately, if the hazardous space is such that people inside the space are not always visible from the reset location, then people inside can be endangered if someone else resets the system. Administrative means such as safety checklists and visual inspections can help, but do not give those inside the space personal control over the reset of the machine.
In simple mechanical systems physical locks are often used to provide personal control over a system. Each worker applies and removes his own lock to the reset switch. The system can not be reset until all the locks have been removed. This straightforward approach has drawbacks, however. Physical locks can damage work in progress (e.g., scratch paint on car bodies) and can be bypassed by anyone with a bolt cutter. Management of unique locks and keys for many workers can be problematic. Also, workers without locks, workers whose locks have been forgotten, and workers whose locks are controlling other machines can not assert control over a machine.
Enabling plugs are also often used. Workers entering the controlled space remove a plug that enables the system to start. The plugs are usually not unique, however, and so systems can be energized while workers are still in danger.
Advanced electronic systems can limit access to an area to specific individuals. These systems must be very complex, however, to verify identity and limit access to pre-approved individuals. Generally a database must be created and managed. Special cards or keys are required to allow the system to identify authorized users. The expense of such systems makes them unrealistic for use with most machines.
There is a need, therefore, for an inexpensive apparatus that gives workers inside a controlled space personal control over the transition of a system from one state to. another (e.g., from halted to energized). The apparatus should not require the workers to carry any additional paraphernalia, and should not be easily defeated by other workers.
The present invention provides an apparatus that allows multiple workers to independently control the energization of a system. The apparatus does not require the workers to carry any additional paraphernalia, and is not easily defeated by other workers. Workers assert control over the system by entering an identifier unique to the worker into the apparatus. Workers release control by entering the same identifier into the apparatus. The apparatus remembers the identifiers associated with assertion of control, and can prevent energization of the system until all the workers that asserted control have subsequently released control. The apparatus can also prevent transition of the system to an undesired state until a desired number of users remain with control asserted. For example, a manufacturing robot can be prevented from energizing until all the users that have asserted control on entering the controlled space have subsequently released control on leaving the controlled space. As another example, a lift can be prevented from operating until an appropriate number of users are on it.
Advantages and novel features will become apparent to those skilled in the art upon examination of the following description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.